Poly(arylene ether) resins are well known and widely used thermoplastics valued for properties including heat resistance, stiffness, and high impact strength. The desire for thermoplastic compositions with increased heat resistance has fueled the discovery of poly(arylene ether) resins with molecular weights and/or monomer composition that enable improved heat resistance as manifested in properties including glass transition temperature, heat distortion temperature, and Vicat softening temperature.
Various methods of preparing poly(arylene ether) homopolymers and copolymers are known. U.S. Pat. No. 3,306,875 to Hay generally describes oxidation of phenols to polyphenylene ethers and diphenoquinones. U.S. Pat. No. 4,011,200 to Yonemitsu et al. generally describes copolymers comprising 50-98 mole percent of 2,6-dimethylphenol monomer units and 50-2 mole percent 2,3,6-trimethylphenol monomer units.
U.S. Pat. No. 4,463,164 to Dalton et al. generally describes a process for production of polyphenylene ethers, comprising oxidatively coupling monohydric phenols in the presence of a complex catalyst and in a liquid medium which is a solvent for the monomer and catalyst and a non-solvent for the polyphenylene ether, forming a slurry of particulate solids containing the polyphenylene ether precipitate, and washing the slurry with an aqueous solution of a chelating agent to remove catalyst residue. The process may utilize solvent recycling.
U.S. Pat. No. 4,556,699 to Bialy et al. generally describes a process for the production of polyphenylene ethers by means of the oxidative polymerization of 2,6-xylenol, with either oxygen or a gas containing molecular oxygen, in the presence of a catalyst, by continuously operating in a circulation system, and with the precipitation of the polymer in the liquid reaction medium. The precipitated polymer is continuously recovered, and part of it may be recycled to the polymerization reactor.
U.S. Pat. No. 4,906,700 to Banevicius generally describes a process for reduction of odoriferous poly(arylene ether) by-products, such as 2,3,6-trimethylanisole, by continuously distilling and recycling the aromatic hydrocarbon solvent used in the poly(arylene ether) polymerization.
There remains a need for a poly(arylene ether) production process that more efficiently utilizes raw materials to form poly(arylene ether) resins that are insoluble in the polymerization reaction mixture. There further remains a need for a poly(arylene ether) production process that efficiently utilizes soluble poly(arylene ether) resins that may be formed in the presence of the desired insoluble poly(arylene ether) resins.
The above-described and other drawbacks and disadvantages of the prior art are alleviated by a process for producing a poly(arylene ether), comprising: oxidatively coupling a monohydric phenol in a reactor using an oxygen-containing gas in the presence of a solvent and a complex metal catalyst to produce a soluble poly(arylene ether) resin and an insoluble poly(arylene ether) resin; separating the soluble poly(arylene ether) resin and the insoluble poly(arylene ether) resin; and recycling a portion of the soluble poly(arylene ether) resin to the reactor.
Other embodiments, including an apparatus for forming a poly(arylene ether) resin, are described below.